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Old 01-11-2011, 01:37 AM   #1
neilgunton
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Is RAID 1 worthwhile?


I am building a new development workstation for myself. Since hard drives are relatively cheap, I'm considering getting two and doing a RAID 1 mirror. Then if one of the drives goes bad, I don't have to spend time manually rebuilding a system from backup (yes, I keep backups, this RAID isn't intended to replace that, but rather to shorten downtime should a drive go bad).

Questions:

1. Does this strategy make sense?

2. The new motherboard (Asus M4A89GTD) will have RAID built in. I have never used motherboard RAID before. Is it generally ok? Since I'm not striping across disks with RAID 1, surely there won't be any issues with having to replace the motherboard with an identical one if I should have to replace it, should there? I mean, the two drives are just mirrors, so shouldn't I be able to use either one standalone?

3. Or, would it be better to use Linux software RAID? If so, why?

4. Does the mobo or Linux RAID speed up reads at all with RAID1, by sharing load across the two disks? In theory, it should be able to, but it just depends on whether it actually does. Anybody know?

This workstation will be using Debian Squeeze, and it will be an AMD Athlon X4 3GHz quad core with 16 GB RAM, 1 TB Samsung SATA hd, Asus M4A89GTD motherboard. I'm getting all that RAM because I'm going to be running MySQL as a slave to my production server, and also want to have ability to run Windows 7 in VirtualBox with resources to spare for disk caching and whatever else I happen to be doing on the host.

Thanks,

Neil
 
Old 01-11-2011, 04:05 AM   #2
Nominal Animal
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A favorite topic of mine!

My /home partition is RAID 1 mirrored, and other partitions RAID 0 striped for performance, using Linux software RAID and ext4 on top of two Samsung 1TB HD103UJ drives. I'm very satisfied in the performance and ease of use. Installed Xubuntu using the alternate install ISO image, and only had to partition the drives; OS installer handled all the rest. (Align your partitions, avoid DOS/CHS compatibility mode.) Oh, and I did tune the mount options. The increase in everyday performance was still a surprise for me.

I haven't had any HD problems yet (11000 hours of active use, 600 spinups, according to smartctl), so I cannot say anything about the downtime in case of problems. I'm considering four Samsung F3 or F4 1T drives using sw-RAID and RAID-10 for another workstation; I do move a lot of scientific data, and really can use the performance.

Quote:
Originally Posted by neilgunton View Post
2. The new motherboard (Asus M4A89GTD) will have RAID built in. I have never used motherboard RAID before. Is it generally ok? Since I'm not striping across disks with RAID 1, surely there won't be any issues with having to replace the motherboard with an identical one if I should have to replace it, should there? I mean, the two drives are just mirrors, so shouldn't I be able to use either one standalone?

3. Or, would it be better to use Linux software RAID? If so, why?
The motherboard has a fake ("BIOS") RAID -- useless, and very typical.
The SATA controllers on this motherboard are provided by AMD SB850 south bridge, which has no real hardware RAID features.

Use Linux software RAID.

Unless you use RAID 5 or 6, software RAID will get you better performance than hardware RAID.
(I'm serious. Many Linux kernel developers use software RAID, and this comes up now and then on the kernel mailing list.)

Quote:
Originally Posted by neilgunton View Post
4. Does ... the Linux RAID speed up reads at all with RAID1, by sharing load across the two disks?
Yes. It depends on the access patterns. A number of concurrent I/O operations get better total bandwidth than a single large/continuous operation; this total bandwidth seems to scale almost linearly with the number of drives up to the hardware bandwidth limits.
(Say, 4 drives with motherboard SATA controllers, 6 on those that have multiple SATA controllers and using separate controllers, and more if using PCIe SATA controllers with the needed bandwidth.)

There are some losses, of course, when using real world filesystems, but ext4 works very well for me. For some, xfs is a better choice.

In any case I wholeheartedly recommend two or four Samsung 1TB drives and Linux sw-RAID, definitely worth the price.
Nominal Animal

Last edited by Nominal Animal; 03-21-2011 at 01:56 AM.
 
Old 01-11-2011, 11:22 AM   #3
neilgunton
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Thanks very much for those tips. I hadn't thought about doing multiple partitions, to be honest - in recent years I've just been putting everything on the one big partition, mostly because it's always a pain to figure out how to split up a big drive. No matter how I do it, it seems I always end up with wasted space in one partition, and not enough space in another. That said, I think it does make a lot of sense to do RAID1 for the root and RAID0 for data partitions (assuming, of course, that you don't care too much if you lose those). The thing with RAID0 is that it multiplies your chances of hard disk failure by the number of disks you're using. It's great for speed, but you need to be fairly certain about your backups.

Anyway, thanks again - it's useful to know that if I do this then I should use the software RAID rather than the mobo.

It's been a while since I looked at Linux RAID documentation - is there any really up-to-date documentation on how to use and manage it? Is the following one current, for example, with what I would find in Debian Squeeze?

https://raid.wiki.kernel.org/index.php/Linux_Raid

Thanks,

Neil
 
Old 01-11-2011, 05:19 PM   #4
jefro
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A backup plan has many parts. I agree that a mirror not only protects data but in some controllers and situations it speeds up data access.

I recommend you get a hardware raid controller if you want to use striping but a mirror on a faux raid controller or software raid is still a consideration for backup use.

Be warned that not all distro's like the faux raid cards. Some may make it difficult to recover using a different live cd.
 
Old 01-11-2011, 07:43 PM   #5
Nominal Animal
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Quote:
Originally Posted by neilgunton View Post
It's been a while since I looked at Linux RAID documentation - is there any really up-to-date documentation on how to use and manage it? Is the following one current, for example, with what I would find in Debian Squeeze?

https://raid.wiki.kernel.org/index.php/Linux_Raid
I've gotten by with just mdadm(8) and mdadm.conf(5) man pages and googling, but there's a lot of excellent advice in the Tweaking,... and Performance sections of the wiki; thanks!
Nominal Animal

Last edited by Nominal Animal; 03-21-2011 at 01:52 AM.
 
Old 01-11-2011, 08:07 PM   #6
jlinkels
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The RAID on the mainboard doesn't work. Maybe it shows it does, later when your server is in production you'll discover it doesn't. Use Linux softraid (mdadm). I have two servers set up like this, and I have seen no performance penalty.

Have a look at these two very useful links:

http://www200.pair.com/mecham/raid/r...aded-etch.html
http://wiki.yobi.be/wiki/Debian_Soft_Raid

It is good that you make backups. However, bare metal restore on a RAID array is difficult if you don't know how to do it. Unless you use backup software taking this into account. If not, be prepared for manual editing of mdadm.conf and fstab after a restore. This is definitely something you want to try before you put the server in production.

jlinkels
 
  


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